The invention relates to cylinder head gaskets as they are used in internal combustion engines.
European Patent Application published as EP 0 627 581 A1 discloses a cylinder head gasket in which two beaded cover plates are provided with a carrier plate located in between. Welded to the carrier plate is a spring travel limiter for protecting the beads, also referred to as a stopper, which extends along the edge of the combustion chamber of the internal combustion engine and also serves for upward extension of the combustion chamber. The cylinder head of the internal combustion engine is thereby being given a defined prestress during clamping-in of the cylinder head gasket along the edge of the combustion chamber. To make the welding easier, the separately produced stopper is initially designed such that it is trapezoidal in section and is then pressed flat to a desired height adjacent to the edge of the combustion chamber, so that it is given mutually parallel bearing in which surfaces for the planar portions of the cover plates radially inwards from the beads. Accordingly, with the initial trapezoidal shape there is no influence on the function of the cylinder head gasket.
In the case of internal combustion engines with less rigid cylinder heads, for instance made of an aluminum alloy, it has been found that a xe2x80x9crolling movementxe2x80x9d of the cylinder head takes place over the width of the stopper. This has the consequence that high edge pressure causes bending and shearing stresses in the cover plates and in the carrier plate of the cylinder head gasket, which may ultimately lead to cracks in the cover plates and in the carrier plate.
German Patent Application published as DE 196 01 324 A1 likewise discloses a metallic cylinder head gasket in which there is provided between two beaded cover plates and a flanged plate with a thickened end portion extending around a combustion chamber opening and formed by folding back a portion of this plate onto the plate. The thus formed flanged portion of the flanged plate is in front of the edges of the cover plates in the radial direction of the combustion chamber opening, so that the flanged portion is not subjected to any pressure. The part of the portion that is effective with respect to the beads has a constant thickness.
German Patent published as DE 195 31 232 C2 discloses a metallic cylinder head gasket in which the flanged portion of the flanged plate forming a stopper of constant thickness for the beads of the cover plates is not provided in the land region between the combustion chamber openings if the land region is very narrow.
It is therefore an object of the invention to provide a cylinder head gasket having a service life which is adversely affected as little as possible by a rolling movement of the cylinder head over the width of the stopper.
The present invention provides a metallic cylinder head gasket for an internal combustion engine having a cylinder head and a cylinder block provided with combustion chambers. The gasket comprises a cover plate which faces the cylinder head when installed and which is provided with one or more openings arranged side-by-side corresponding to the combustion chambers of the internal combustion engine. The cover plate has a bead extending around each opening with a space between the bead and the combustion chamber. This leaves a straight sheet metal portion in the edge region of the opening. A stopper for protecting the bead is arranged adjacent to the bead around each opening radially inwards from the respective bead. The apex of the bead faces away from the cylinder head. The stopper forms a seal portion of increased height wherein the stopper decreases in its thickness radially outwards by a decrease in material thickness in such a manner that the surface pressure in the region of the stopper is essentially homogeneous over the width of the stopper under operating conditions.
The edge pressure is reduced by corresponding beveling of the stopper. This has the consequence that the bending and shearing stresses in at least one cover plate and in a carrier plate, if provided, can be reduced. Consequently, the risk of cracks in the cover plates and in the carrier plate can be reduced. Instead of localized forces on a small area, forces are distributed over a larger surface area is obtained. Consequently, there is a lower partial pressure between the cylinder head and the facing cover plate and, as a result of this, less wear. The stopper is consequently adapted to the deformation of the cylinder head. Adaptation to different cylinder head rigidities is possible by correspondingly changing the angle of the beveling. The angle of the beveling is determined by means of clamping-in tests.
The invention is explained in more detail below with reference to exemplary embodiments represented in the attached drawings.